Certain radio systems such as, for example, the so-called “GPS” (standing for “Global Positioning System”) satellite navigation system use spread spectrum, hence broadband, radio signals received with a very low power level, easily, from 30 dB to 40 dB below the level of thermal noise at the input of a receiver. In a favourable environment, that is to say one which is not very noisy, the despreading operation enables the signal-to-noise ratio of the signal received to be raised well above 0 dB.Hz, so that the signals received may be utilized safely.